Solid catalysts (Heterogeneous catalysts) have been industrialized in the early 20th century and since then have contributed to the development in the inorganic chemical industry, the coal chemical industry and the petrochemical industry. Solid catalysts can be generally classified into three categories according to the material system: metal sulphides used for hydrodesulphurization of petroleum, metal oxides used for selective oxidation of unsaturated hydrocarbons and metals used for purification of automobile emissions. Among others, noble metals have broad utility because they can be used for both oxidation and reduction reactions. Typical noble metals particularly include palladium and platinum.
Gold has been recognized as a metal that is particularly stable and thus has poor catalytic activity among noble metals. However, the present inventor found for the first time in the world that gold nanoparticles having a diameter of 5 nm or less exhibit superior catalytic activity when they are supported on oxides of base metals (Non Patent Literature 1). Gold nanoparticles exhibit high performance, which could not be attained by palladium or platinum catalysts, in CO oxidation at room temperature, gluconic acid synthesis by oxygen oxidation of glucose aqueous solution, hydrogen peroxide synthesis from hydrogen and oxygen, one-pot synthesis of azobenzene from nitrobenzene and the like.
Various catalysts containing noble metals have been proposed. For example, Patent Literatures 1 and 2 propose noble metal-containing catalysts having selectivity in specific types of reactions.    Patent Literature 1: Japanese Patent Application Laid-open No. 2007-301470    Patent Literature 2: Japanese Patent Application Laid-open No. 2007-90164    Non Patent Literature 1: M. Haruta, Chem. Lett. 1987